Put chicken in a 6-quart pot. Add just enough water to cover. Bring to a boil, reduce heat to low and simmer 8 to 10 minutes, until chicken is no longer pink in the center. Remove with tongs or a slotted spoon to a cutting board and cool. Reserve cooking liquid and set aside. Mix mayonnaise, water, barbecue sauce, vinegar, chives, garlic powder and pepper in a large salad bowl until blended. Add enough water to the poaching liquid in pot to cook pasta (you need about 4 quarts). Bring to a boil. Add pasta and cook 9 minutes or until firm-tender. Drain well. While pasta boils, cook bacon in a skillet (or microwave) until crisp. Drain on paper towels. Cut into small pieces. Add hot pasta to the dressing in the salad bowl and toss to mix and coat. Cut chicken into bite-size pieces and add to the salad bowl, along with the bacon, lettuce and tomato. Toss gently to mix. Serve warm.